Testing the hypothesis that heart rate and respiration, via varo-receptor- and chemoreceptor-feedback to the central nervous system, directly influences sensorimotor behavior, the following experiments are planned: (1) The effect on reaction time and threshold signal detection performance of simultaneously measured respiraotry phase and time of stimulation within the cardiac cycle will be determined; (2) The effects of stimulation of the carotid sinus nerve and the aortic depressor nerve on evoked potentials in nucleus cuneatus, will be determined in acute cat preparations; (3) The role of respiratory changes and metabolic demands in producing anticipatory cardiac decelerations will be evaluated by breath-by-breath measurements of oxygen consumption; (4) Pilot studies will be made of the possibility of producing in cats an analog of the finding in humans that operant behaviors are emitted later and later in the cardiac cycle as heart rate increases. If successful, the effects of sino-aortic denervation on this phenomenon will be determined. Continued studies will be made of differential cardiac slowing in man as a function of time of stimulus placement within the cardiac cycle, attention being given to variations of stimulus-significance and concomitant variations in the P300 complex in averaged auditory evoked potentials.